I read this book at least 15 years ago, maybe longer. I don’t think it was new when I read it.

The cover was a cutout of a body and the body was a page in a book with words all over it.

The protagonist is a boy living in the sewers (or vents?) who is part of a gang, but fairly removed from them. The gang leader likes him which is why he is allowed to hang around. I think everyone is addicted to some kind of technology and he prefers to read which is why they think he’s weird.

There’s a ton of pollution and all of the rich people have moved either to another planet or a bubble where they are protected from the pollution.

He’s an orphan and was in a foster home for awhile. I don’t think he liked the foster family and that’s why he ran away. He was close with his foster sister but she’s sick and all she wants to do is see the blue sky (which she can’t because of all of the pollution). Somehow she ends up with the protagonist on the other planet/bubble so she can get better.

It turns out the gang leader is the protagonists dad and that’s how it ends?